There is a widespread need for inspection data for electronic parts in a manufacturing environment. One common inspection method uses a video camera to acquire two-dimensional images of a device-under-test.
Height distribution of a surface can be obtained by projecting a light stripe pattern onto the surface and then reimaging the light pattern that appears on the surface. One technique for extracting this information based on taking multiple images (3 or more) of the light pattern that appears on the surface while shifting the position (phase) of the projected light stripe pattern is referred to as phase-shifting interferometry, as disclosed in U.S. Pat. Nos. 4,641,972 and 4,212,073 (incorporated herein by reference).
The multiple images are usually taken using a CCD (charge-coupled device) video camera with the images being digitized and transferred to a computer where phase-shift analysis, based on images being used as “buckets,” converts the information to a contour map (i.e., a three-dimensional representation) of the surface.
The techniques used to obtain the multiple images are based on methods that keep the camera and viewed surface stationary with respect to each other while moving the projected pattern.
One technique for capturing just one bucket image using a line scan camera is described in U.S. Pat. No. 4,965,665 (incorporated herein by reference).
U.S. Pat. Nos. 5,398,113 and 5,355,221 (incorporated herein by reference) disclose white-light interferometry systems which profile surfaces of objects.
In U.S. Pat. No. 5,636,025 (incorporated herein by reference), an optical measuring system is disclosed which includes a light source, gratings, lenses, and camera. A mechanical translation device moves one of the gratings in a plane parallel to a reference surface to effect a phase shift of a projected image of the grating on the contoured surface to be measured. A second mechanical translation device moves one of the lenses to effect a change in the contour interval. A first phase of the points on the contoured surface is taken, via a four-bucket algorithm, at a first contour interval. A second phase of the points is taken at a second contour interval. A control system, including a computer, determines a coarse measurement using the difference between the first and second phases. The control system further determines a fine measurement using either the first or second phase. The displacement or distance, relative to the reference plane, of each point is determined, via the control system, using the fine and coarse measurements.
Current vision-inspection systems have many problems. Among the problems are assorted problems associated with current mechanical translation devices associated with vision-inspection systems. Among the mechanical translation problems are that the trays of devices, such as trays of semiconductor chips, associated with current vision-inspection systems must be flipped by hand since both sides of the devices must be inspected. In current systems, the flipping of trays of devices is done by an operator. Operator intervention requires time and may be prone to error. Throughput of the machine-vision-inspection system may also be affected. For example, if the operator is on break or otherwise unavailable, throughput of the machine-vision-inspection system suffers since the machine is stopped awaiting operator intervention. As mentioned, errors can also occur as a direct result of operator intervention. When both sides of the part need to be inspected the parts must be flipped. If the operator is interrupted while flipping the trays, the operator may forget the orientation of the devices or trays after the interruption. In other words, due to the interruption, the tray carrying the devices may not be flipped. At best, the subsequent operation will detect that the devices are not flipped if the machine-vision-inspection system has the capability to detect that the wrong portion of the device is presented for inspection. In this event, more time is lost since the operator must now flip the unflipped trays. This of course also negatively affects throughput of the machine-vision-inspection system. At worst, the machine-vision-inspection system would not detect that the wrong side of the device (same side of the device previously inspected) was again being inspected. In other words, the inspection would be repeated. The result would be far worse in that devices that would not pass the inspection would be shipped to customers or placed in larger devices shipped to customers. If the products are caught by a subsequent sampling, the larger devices would have to be reworked. If the products were not caught be a subsequent sampling or inspection, defective product may be shipped to a customer. This of course is devastating in a world where product quality is constantly stressed by marketing executives. Even a hint of less than top quality can devastate the market for a product.
To overcome the problems stated above as well as other problems, there is a need for an improved machine-vision system and more specifically for a machine-vision-inspection system capable of flipping trays of devices without operator intervention. In addition, there is a need for a flipping device that operates to reliably flip the trays of devices so that all portions of the devices within the trays are reliably inspected. In addition, there is a need for a flipping device that facilitates automated high-speed three-dimensional inspection of objects in a manufacturing environment. There is also a need for a device that is easily accommodated as a station on an automated manufacturing line.